The present invention relates to the field of substance identification from a remote location. More particularly, the invention provides significant improvements over previous U.S. Pat. No. 4,922,467, issued on May 1, 1990. The original patent disclosed an acoustic detection apparatus for characterization of an object within an enclosure, or buried beneath the ground. For this purpose, U.S. Pat. No. 4,922,467 disclosed an apparatus that transmits acoustic energy towards the object, and subsequently detects and analyzes the energy reflected and refracted/transmitted by the object. By comparing the transmitted, reflected, and refracted/transmitted energy, the apparatus can assign a signature to the object, and compare the signature with a database of signatures of known objects, thus identifying the object.
The apparatus of the present application provides significant improvements over the original patent, by allowing highly accurate characterization of a substance that is enclosed within a container. The improved material classification technique involves application of acoustic or electromagnetic (EM) energy to the container, and detection of both the reflected and refracted/transmitted energy therefrom. Subsequent analysis of the time and energy content of the detected signals allows computation of acoustic/EM energy impedance, acoustic/EM energy absorption, and acoustic/EM wave velocity changes that are conferred on the reflected and transmitted/refracted signals by the presence of the substance. These values allow sound predictions to be made regarding the mechanical properties of the substance, thus providing the substance with a specific signature. Comparison of the signature with a database of known signatures permits identification of the substance. The present invention can also analyze the absorption characteristics of the substance over a range of frequencies. In this way, the apparatus allows computation of additional parameters involving absorption as a function of frequency. These additional parameters allow the formulation of a highly detailed signature for each substance. The improvements over U.S. Pat. No. 4,922,467 therefore permit the apparatus to identify a considerably wider range of substances with increased accuracy. For specific classes of substances, analysis of the absorption/frequency characteristics alone can be sufficient for accurate substance identification.
Analysis of reflected acoustic energy is well known in the art to facilitate identification of a substance concealed beneath an outer layer. For example, U.S. Pat. No. 5,979,240 issued Nov. 9, 1999, discloses a device for detecting recyclable plastic and metal items within solid waste. Acoustic energy of a fixed wavelength is transmitted into the waste causing specific substances to resonate. Detection of the resonating energy allows the recyclable items to be located. Other such devices are directed towards medical uses. For example U.S. Pat. No. 4,855,911 issued Aug. 8, 1989, provides a device for transmitting ultrasound into tissues and detecting the back-scatter energy reflected from buried anomalies within the tissue. Still further devices, such as those disclosed by U.S. Pat. No. 5,563,848 issued Oct. 8, 1996, and U.S. Pat. No. 5,974,881 issued Nov. 2, 1999, detect the presence of objects buried within the ground. Sound waves are transmitted into the ground, and the nature of the energy reflected by the buried object is detected and analyzed.
It is important to note that the devices disclosed by the cited references specifically involve detection of reflected acoustic energy. By limiting analysis to reflected energy, the parameters for substance determination are limited. For this reason, U.S. Pat. No. 4,922,467, which is incorporated herein by reference, provides a preliminary means for material classification by simultaneous analysis of both reflected and refracted/transmitted acoustic energy, thus providing each substance with a unique and characteristic signature. The present application further expands and refines the accuracy and flexibility of the apparatus disclosed by U.S. Pat. No. 4,922,467. The improved apparatus therefore provides both rapid and highly accurate substance determination.
In accordance with the present invention, xe2x80x9cenclosurexe2x80x9d is defined as being a hollow box-like structure containing an object to be detected and identified with respect to its constituents. The apparatus disclosed permits reliable, accurate and non-invasive identification of enclosed materials, and can have a number of important applications.
In a first embodiment, the present invention provides a means for detecting illegal substances such as drugs and explosives within suitcases and baggage, without the need for time-consuming human intervention. Current systems for analyzing the contents of a suitcase include X-ray scanning machines and animals trained for chemical sniffing. However, these systems are labor intensive. Moreover, visual scanning of X-ray images is prone to human error, since illegal substances may appear similar to those which are legal. Animals can be trained to detect the scent of specific chemicals, but the number and range of substances may be restricted, and such substances may be masked by other smells to prevent their detection. It is therefore desirable to develop more accurate, automated techniques for the detection of illegal substances within suitcases and other baggage. In particular, by using a wider frequency range of energy input (including EM radiation), and by analyzing energy absorption properties over a range of frequencies, the present invention permits highly accurate identification of substances within an enclosure. The devices of the present invention may be arranged as an array over a conveyor, thus mapping the contents of the suitcases as they are transported horizontally along the conveyor. In addition, the present apparatus does not require shielding from the operator or public, since harmless acoustic or electromagnetic energy may be used by the device. This contrasts with the X-ray devices presently used for luggage analysis, which require shielding and potentially dangerous radiation.
In a second embodiment, the invention may be used to detect the presence of substances buried beneath the surface of the earth. For example, the apparatus of the present invention can determine the location of pipelines or other enclosures containing oil, gas or chemicals. Importantly, once the enclosure or pipeline has been located, the present invention may be used to quickly and accurately characterize the nature of the substance contained within the enclosure or pipeline. In this regard, it is well known in the art that acoustic waves may be bounced off the ocean floor, in order to determine the nature of the material from which sediment layers are comprised. The present invention provides for significant additions and enhancements to these previous techniques, permitting the formulation of detailed signatures for different types of substances.
In a third embodiment, the invention may be used to detect the presence of explosives buried beneath the ground. For example, a potentially explosive land mine may be differentiated from spent shrapnel or other scrap metal by the detection of explosive substances enclosed within the body of the mine. The invention presents a significant advantage in that the mine may be detected and characterized whilst still underground, without the need for disturbing the mine and risking detonation.
The apparatus of the present invention comprises a transmitter device for directing a pulse of EM or acoustic energy towards the enclosure that contains the unknown substance. The energy may be in the form of a specific pulse, or may be random noise. The energy is reflected from any intercepted interface, which may include the surface of the enclosure, and the surface of the substance to be detected within. The duration and intensity of the reflected energy can be detected by a first receiver (EM or acoustic). A proportion of the EM or acoustic energy is also refracted and/or transmitted from the substance within the container, and the duration and intensity of this refracted/transmitted energy may be detected by a second receiver. When a pulse of initial energy is transmitted towards the object, specific features of the reflected and refracted pulses can be measured and compared with the original pulse. When random noise is used, more complex processing may be carried out by correlation techniques that are well known in the art. In this way, the incident, reflected, and transmitted/refracted random noise energy can be compared and differentiated from background noise.
A signal processor, connected to the transmitter and the first and second receivers, processes the information regarding the transmitted and received energy, thus producing an object signature indicative of the substance. A comparator is also provided to compare the object signature with those of known substances stored in a computer database. The computer determines a match, or a closest possible match, thus identifying the substance.
The optional use of EM transmitters and receivers in the apparatus of the present invention greatly enhances the scope of signature matrices that may be provided for a particular substance. Moreover, the present invention significantly improves the accuracy and range of material types that may be detected and characterized. This is attributable in part to the capacity of the apparatus to transmit and receive energy of varying frequencies. Thus over a range of frequencies the absorption characteristics of the substance may be determined. By analysis of the rate of change of absorption with respect to frequency, additional important information regarding the mechanical properties of the substance is provided, greatly enhancing the detail of the substance signature. Moreover, the detailed signature provides a more refined and accurate representation of the substance, permitting a much larger range of substances to be differentiated from one another.
In accordance with one aspect of the invention there is provided an apparatus for detecting the substance of an object contained within an enclosure, the apparatus comprising: electromagnetic or acoustic energy transmitter means for transmitting at least two pulses of electromagnetic or acoustic energy at a first side of the enclosure; first electromagnetic or acoustic energy receiver means for receiving electromagnetic or acoustic energy that has been reflected from the object to produce at least two reflected electromagnetic or acoustic energy signals; second electromagnetic or acoustic energy receiver means for receiving electromagnetic or acoustic energy that has been transmitted or refracted through the object to produce at least two transmitted or refracted electromagnetic or acoustic energy signals; signal processor means connected to said transmitter means and to said first and second receiver means for producing an object signature, wherein said object signature is generated by computing energy absorption for each frequency and calculating a rate of change of said energy absorption as a function of frequency; and comparator means for comparing said object signature with signatures of known objects to determine the substance of said object.
In accordance with another aspect of the invention there is provided an apparatus for detecting the substance of an object contained within an enclosure, the apparatus comprising: electromagnetic energy transmitter means for transmitting a pulse of electromagnetic energy at a first side of the enclosure; first electromagnetic energy receiver means for receiving electromagnetic energy that has been reflected from the object to produce a reflected electromagnetic energy signal; second electromagnetic energy receiver means for receiving electromagnetic energy that has been transmitted or refracted through the object to produce a transmitted or refracted electromagnetic energy signal; signal processor means connected to the transmitter means and to the first and second receiver means, the signal processor means processing the transmitted pulse of electromagnetic energy, the reflected electromagnetic energy signal, and the refracted or transmitted electromagnetic energy signal to produce an object signature indicative of the object; and comparator means for comparing the object signature with the signature of known objects to determine the substance of the object.
In accordance with still another aspect of the invention there is provided a method of determining the substance of an object located within an enclosure, the method comprising the steps of: applying at least two pulses of electromagnetic or acoustic energy each of known intensities and differing frequencies to a first side of the enclosure and the object in the enclosure; detecting at least two pulses of reflected electromagnetic or acoustic energy reflected from a surface of the object to provide reflected electromagnetic or acoustic energy signals; detecting at least two pulses of transmitted or refracted electromagnetic or acoustic energy transmitted or refracted through the object to provide transmitted or refracted electromagnetic or acoustic energy signals; processing the reflected and transmitted or refracted electromagnetic or acoustic energy signals to produce an object signature, the object signature comprising the electromagnetic or acoustic energy absorption of the substance as a function of frequency; and comparing the object signature so obtained with signatures of known objects to determine the substance of the object.
In accordance with yet another aspect of the invention there is provided a method of determining the substance of an object located within an enclosure, the method comprising the steps of: applying a pulse of electromagnetic energy of a known level to a first side of the enclosure and the object in the enclosure; detecting the reflected electromagnetic energy reflected from a surface of the object to provide a reflected electromagnetic energy signal; detecting the transmitted or refracted electromagnetic energy transmitted or refracted through the object to provide a transmitted or refracted electromagnetic energy signal; processing the reflected and transmitted or refracted electromagnetic energy signals to produce an object signature; and comparing the object signature so obtained with signatures of known objects to determine the substance of the object.